Power semiconductor devices are currently being used in many applications, either as discrete components or integrated with other transistors as an integrated circuit. Such power devices include high-voltage integrated circuits which typically include one or more high-voltage transistors, often on the same chip as low-voltage circuitry. A commonly used high-voltage component for these circuits is a laterally diffused metal oxide semiconductor (LDMOS) transistor. High-power applications have called for the use of such lateral double diffused MOS transistors primarily because they possess lower “on” resistance, RDS (on), faster switching speed, and lower gate drive power dissipation than their bipolar counterparts. However, these devices have heretofore also been strongly associated with bi-polar based process flows when integrated into a Bi-CMOS environment.
LDMOS transistors used in the high-voltage integrated circuits may generally be fabricated using some of the same techniques used to fabricate low voltage circuitry or logic circuitry. In general, LDMOS structures are fabricated in a thick epitaxial layer of the same or opposite conductivity type as the substrate. The epitaxial layer helps to equally distribute the applied drain voltage laterally across the silicon surface.
Typically, in a step subsequent to the formation of the epitaxial layer, a gate structure is formed over the epitaxial layer and a drain region dopant is laterally diffused under the gate structure. Diffusing the drain region dopant generally requires a masking step that masks all regions of the device except for the drain region and the gate structure. In addition to laterally diffusing the drain region dopant, a source region dopant is laterally diffused under the other side of the gate structure. An additional masking step, similar to the masking step previously described, is also required when laterally diffusing the source region dopant. Subsequent to laterally diffusing the source and drain region dopants, a higher concentration dopant may be diffused within the device. The previously described method of manufacturing an LDMOS device is extensively used and well accepted, however, it may be very time consuming and costly. More specifically, it is known that the multiple masking steps required to laterally diffuse the source and drain region dopants may be time consuming and costly.
Accordingly, what is needed in the art is a method of manufacturing an LDMOS device that does not experience the time and cost issues associated with the prior art methods of manufacturing LDMOS devices.